Achromatic Test Research Articles

Establishment and decay of orientation-contingent aftereffects of color

We have used a null method to measure the orientation-contingent aftereffects of color first described by McCollough. After alternately inspecting, for example, a green horizontal line grating and a magenta vertical line grating, the Os report that in achromatic test gratings the horizontal lines appear pinkish and the vertical lines appear greenish. We have used a special color-mixing projector to add variable amounts of green and magenta light to the test gratings until they appear matched and nearly achromatic. The colorimetric purity needed to achieve this null setting is a quantitative measure of the strength of the colored aftereffect. Following inspections of the colored patterns ranging from 15 sec to 150 min, six Os showed aftereffects lasting from a few minutes to 7 or more days. The indices of colorimetric purity increase with inspection time and decline with time after inspection. The decay function is not quite linear either on semilog or on log-log coordinates. The rate of decay is mainly dependent on the magnitude of the effect built up during inspection. We conclude that the buildup and decay of these aftereffects show some of the time characteristics usually associated with central adaptability rather than sensory adaptation.

Curvature as a feature of pattern vision.

Prolonged inspection of convex lines of one color and concave lines of another color can cause the appearance of oppositely colored aftereffects in curved, achromatic test lines. These effects, strongly dependent on radius of curvature, cannot be attributed to tilt or orientation. It is concluded that these results are not encompassed by models of the visual system that are based on rectilinear arrays and that curvature is a specific feature of human visual perception.

Spatial frequency dependent chromatic after-effects.

McCOLLOUGH1 first reported that following prolonged inspection of vertical gratings on orange backgrounds successively alternating with horizontal gratings on blue backgrounds, the vertical stripes in an achromatic test pattern will appear greenish and the horizontal stripes will appear pink. Because the effect was evidently related to the orientation of the grids on the retina, McCollough hypothesized that it was due to adaptation or fatiguing of colour- and orientation-specific edge detectors in the visual system. But recent studies2–4 employing two grids of varying spatial frequency but with the same orientation have demonstrated similar chromatic after-effects on achromatic test patterns of the same orientation.

The effect of movement on the perceived brightness of chromatic afterimages

The present study explored the effects of adaptation to static and moving chromatic stimuli on the perceived brightness of afterimages projected on static and turning achromatic test stimuli The Ss were presented with two stimuli of the same color to which they adapted for 1 min. The Ss then reported the brightness of their afterimages when viewing achromatic stimuli. A rotating stimulus, viz, 16, 45, or 78 rpm. was compared with a stationary stimulus. Results indicate that (a) the introduction of movement detracts from the brightness of an afterimage, and (b) a speed of 45 rpm affects the afterimage more than 16 or 78 rpm.

Brightness Scaling of White and Colored Stimuli

Brightness scales for chromatic and achromatic test stimuli have been obtained by the methods of ratio production and magnitude estimation for the dark-adapted observer and conditions of brief foveal stimulation. All scales adhere to the form of a power law for brightness, and scales obtained under the differing psychophysical procedures agree.

Brightness scaling of white and colored stimuli.

Brightness scales for chromatic and achromatic test stimuli have been obtained by the methods of ratio production and magnitude estimation for the darkadapted observer and conditions of brief foveal stimulation. All scalesadhere to the form of a power law for brightness, and scales obtained underthe differing psychophysical procedures agree.